Transport And Transformation Characteristics Of Phosphorus In The Lower Reaches Of The Yellow River From Xiaolangdi To Huayuankou

The complex topography of the lower reaches of the Yellow River from Xiaolangdi to Huayuankou,the establishment of Xiaolangdi reservoir and the operation of water and sand transfer have changed the changes of water-sand process in the Xiaohuajian inter-river section,which affects the material cycling process of total phosphorus with water-sand as the transport carrier.In this study,the transport and transformation characteristics of phosphorus in the Yellow River section from Xiaolangdi to Huayuankou were studied more systematically by using data collection and indoor experimental simulation.In this study,hydrological data such as runoff,sand content and total phosphorus data were collected and collated from five state-controlled cross-sections,including Xiaolangdi,Huayuankou,Baimasi,Longmenzhen and Wuzhiqushou,and the characteristics of the changes in water and sand conditions and total phosphorus concentration in water were analyzed.By using indoor simulation experiments,the phosphorus adsorption characteristics of sediment under different sand content and initial phosphorus concentration conditions were investigated,while quasi primary and quasi secondary kinetic models of water body adsorption were constructed and the types of sediment physicochemical adsorption were analyzed.Through the analysis of phosphorus sources in the Xiaohuajian River section,the contribution of each input pathway to phosphorus fluxes and the correlation between changes in water-sediment processes and phosphorus fluxes in the Xiaohuajian River section were explored in depth,and the transport and transformation characteristics of phosphorus in the Xiaohuajian River section were systematically explained.The main conclusions of this study are as follows:(1)The annual average runoff of Xiaolangdi Reservoir and Huayuankou section in the past 20 years presents a state of fluctuation,and the variation of the flow is unbalanced.The inter-annual variation of the runoff of Xiaolangdi Reservoir and Huayuankou section is not synchronous.The sediment content of Xiaolangdi Reservoir and Huayuankou section decreased in the past 20 years.The seasonal variation of runoff and sediment transport was significant,but the seasonal variation of total phosphorus concentration was not significant,and its concentration was between classⅠand classⅢsurface water.The seasonal variation process of water and sediment in the area from Xiaolangdi to Huayuankou of the lower Yellow River from 2018 to 2021 was not synchronized with the seasonal variation process of phosphorus concentration.The variation of water and sediment was consistent with the natural variation rule,and the variation of phosphorus concentration was interfered by human factors.(2)The effect of low sediment content(0.5-2 kg/m~3)on phosphorus adsorption by suspended sediment of the Yellow River was not significant under the state of dynamic water disturbance.Under the condition of higher sediment content(10-90kg/m~3),the adsorption rate and total adsorption capacity of suspended sediment in the Yellow River are faster and larger with the increase of sediment content.There is a logarithmic relationship between the removal rate of total phosphorus and the sediment content.The removal rate increases with the increase of sediment content,and the sediment content is positively correlated with the adsorption capacity and the removal rate.However,with the increase of sediment content,the phosphorus adsorption of Yellow River sediment per unit mass becomes less significant and decreases logarithmically.(3)Under the condition of dynamic water disturbance and high sediment content,the phosphorus adsorption capacity of suspended sediment in the Yellow River increased with the increase of initial phosphorus concentration.Under the same condition of high sediment content,the removal rate of phosphorus from suspended sediment of the Yellow River showed a V-shaped trend with the increase of initial phosphorus concentration.In the disturbed state of water,the phosphorus adsorption process of sediment is mainly physical adsorption,and there is also a certain chemisorption,and the adsorption rate has no obvious correlation with the sediment content.The chemisorption effect of suspended sediment in the Yellow River is sensitive to the initial phosphorus concentration.(4)From 2018 to 2020,the phosphorus flux between floret showed an increasing trend,which was greatly affected by the seasons.Through the analysis of TP sources among small flowers,it can be seen that the contribution rate of TP input in descending order is Xiaolangdi Reservoir>agricultural planting source>domestic sewage source>tributary.The P flux is positively correlated with the change of water and sediment,and the influence of runoff on P flux is greater.